In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure of radial rays such as light or an electron beam through a mask having a predetermined pattern, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film.
A resist material in which the exposed portions become soluble in a developing solution is called a positive-type, and a resist material in which the exposed portions become insoluble in a developing solution is called a negative-type.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization.
Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are now starting to be introduced in mass production. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having a wavelength shorter than these excimer lasers, such as F2 excimer lasers, electron beams, extreme ultraviolet radiation (EUV), and X rays.
Resist materials for use with these types of exposure light sources require lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources.
As a resist material which satisfies these conditions, a chemically amplified resist is used, which includes a base resin that exhibits a changed solubility in an alkali developing solution under action of acid and an acid generator that generates acid upon exposure.
For example, a chemically amplified positive resist contains, as a base resin, a resin which exhibits increased solubility in an alkali developing solution under action of acid, and an acid generator. In the formation of a resist pattern, when acid is generated from the acid generator upon exposure, the exposed portions become soluble in an alkali developing solution.
Currently, resins that contain structural units derived from (meth)acrylate esters within the main chain (acrylic resins) are widely used as base resins for resists that use ArF excimer laser lithography, as they exhibit excellent transparency in the vicinity of 193 nm (for example, see Patent Document 1). Here, the term “(meth)acrylic acid” is a generic term that includes either or both of acrylic acid having a hydrogen atom bonded to the α-position and methacrylic acid having a methyl group bonded to the α-position. The term “(meth)acrylate ester” is a generic term that includes either or both of an acrylate ester having a hydrogen atom bonded to the α-position and a methacrylate ester having a methyl group bonded to the α-position. The term “(meth)acrylate” is a generic term that includes either or both of an acrylate having a hydrogen atom bonded to the α-position and a methacrylate having a methyl group bonded to the α-position.
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2003-241385